Severe developmental delay and epilepsy in a Japanese patient with severe congenital neutropenia due to HAX1 deficiency.

HAX1 deficiency has recently been identified as a cause of severe congenital neutropenia (SCN), but little is known about the phenotype. We described an SCN patient with a homozygous 256C-to-T transition causing an R86X mutation in the HAX1 gene. Notably, the patient has been complicated by epilepsy and severe delay of motor, cognitive, and intellectual development; each developmental quotient was 21-26 at 7 years old. Growth failure and dental development delay were also noted. Neurodevelopmental delay in this patient expands the clinical phenotype of HAX1 deficiency and suggests an important role of HAX1 on neural development as well as myelopoiesis.